Explosive cutter for parachute lines



g- 1959- J. A.STUPIAN v 2,897,799 7 EXPLOSIVE CUTTER FOR. PARACHUTE muss Filed July 29, 1957 figi P 5a, 55

INVENTOR. Joe )4. 57'uP/A/v id States 2,897,799 Patented Aug. 1959 EXPLUSKVE CUTTER FOR PARACHUTE LINES Application July 29, 1957, Serial No. 674,880

1 Claim. (Cl. 123-24) This invention relates generally to explosive cutters for parachute lines, and more particularly to an explosive cutter in which the firing pin spring is compressed and a breakaway joint in the firing pin is released by the firing pull.

Parachute dropping of personnel, equipment, and supplies has become a highly developed art and a highly developed technology developed in the past mostly for military operations by parachute troops. Recently, the development of practical parachute dropping equipment has initiated the use of the military parachute dropping techniques for civilian applications, for example, in fighting forest fires. in either case, accuracy of dropping on target requires that the drop be free falling during the initial period of flight and that the fall be broken by parachute only at the last safe moment. Other considerations also require a delay in opening the main parachute which breaks the fall of the dropped object. The premature opening of the parachute might result in entanglement with the dropping plane or other planes in the same formation. Military considerations make it advisable to reduce to a minimum the time of slow moving exposure after the main parachute has opened. The foregoing and other considerations have resulted in the standard method of dropping which involves opening a small pilot parachute as soon as the dropped object leaves the dropping plane, and the release of the main parachute only after a predetermined number of seconds of free fall, depending on the altitude from which the drop is made.

While various methods for releasing the main parachute after a desired period of free fall have been pro posed, perhaps the most promising and practical device is a line cutter carried on the reefing line of the main parachute and adapted to cut the reefing line and release the parachute when actuated by an explosive charge. The present invention relates to an explosive reefing line cutter in which the pilot chute, or some other initial operating means, discharges a striking pin against a primer contained within the cutter, and the primer initiates the burning of a delay train, preferably comprised of a series of pellets of special slow burning powder, which, like a fuse, requires a predetermined number of seconds to bring the ignition spark to the charge of cutter-actuating explosive.

The explosive cutters heretofore known have combined two very undesirable characteristics: (1) they have proven very unreliable in operation; (2) they have been expensive to make.

The principal causes for operating failure of the explosive cutters has proven to be the firing mechanism, rather than the burning of the delay train, the firing of the explosive charge, or the cutting of the reefing line. Typical of the specifications for safe operation of the striking pin means of an explosive cutter are the double tests that it must, on the one hand, not be unintentionally operated by normal manual handling,

while, on the other hand, it must fire promptly and unfailingly when subjected to the usual operating pull on the release mechanism. For example, one standard military specification requires that the pull mechanism be able to resist a pull of ten pounds without functioning; and at the same time the pull mechanism must fire when subjected to a pull equivalent to that exerted by a twenty pound weight dropped through a distance of three inches. The first of the two tests practically eliminates operation by hand, while the second insures operation by pilot parachute.

It is a problem encountered generally in all such trigger mechanisms that construction may be expensive and complex if it is to operate unfailingly in a desired manner. Cheap release mechanisms fail to have the discrimination between non-operating and operating pulling force, whereas complex and expensive mechanisms tend to jam.

The tendency of the release mechanism to jam or operate improperly is often proportional to the amount of stored potential energy in the spring mechanism. If the spring is highly compressed and all the striking energy required for firing is. stored in the device at the time of assembly, tendency to jam seems to be greater than in firing mechanisms in which the firing pin is reciprocated to compress the spring at the time of firing; this may be traceable to the problem of metal particles or burr shavings in the apparatus which jam the former type of construction, but are loosened by the operation of the latter.

Another objection to explosive cutters has been that it was believed necessary for the firing mechanism to be prearmed, release being triggered by the pilot chute pull. Prearmed assemblies are generally objectionable from a safety viewpoint.

It is a major object of the present invention to provide an explosive cutter particularly suitable for cutting the reefing line of a main parachute a predetermined number of seconds after a firing mechanism in the cutter has been subjected to a pull by the opening of the pilot chute.

It is another major object of the invention to provide a reefing line cutter with a firing mechanism which is practically unfailing in operation.

Still another object of the invention is to provide a cutter firing mechanism in which the striking pin spring is not fully compressed at the time of assembly, and in which the striking pin undergoes a cycle of reciprocation at the time of firing by the pull of the pilot chute.

Another object of the invention is to provide a cutter firing pin which is constructed in two sections which separate on firing.

Finally, it is an object of the invention to provide an explosive cutter which is of simple and inexpensive construction and can be assembled without threaded assembly of the members.

The foregoing and other objects of the invention are accomplished by the employment in the cutter assembly of a firing mechanism in which the striking head is carried on a firing pin shaft which is comprised of two parts reciprocable as one in a firing pin cylinder, but instantly breaking away from each other it retracted sutficiently from the firing pin cylinder. The general idea of the invention will best be understood from the followiug illustrative application of it in one specific embodiment described below in connection with the accompanying drawings, in which:

Figure 1 is a view of an explosive reefing line cutter just prior to operation, showing both the pilot chute connection and the location of the reefing line to be cut;

Figure 2 is a longitudinal sectional view of the explosive cutter;

Figure 3 is a perspective view of the two parts of the striking pin shaft; and,

Figure 4 is a perspective view of the striking pin cylinder and the striking pin spring.

The explosive cutter is indicated by the numeral and is seen to be a tubular device, usually about five inches long and three-quarters of an inch in diameter. A fiat nylon ribbon parachute reefing line 11 passes through the cutting end 12 of the cutter It by way of a pair of reefing line holes 13 and 14. The opposite end of the cutter 10 is the firing end 15, a connection eye to which a pilot parachute line 17 is attached.

In Figure 1, the cutter 10 is shown with the safety screw 18 (see Figure 2) removed from the safety screw hole 19 and the locking cotter pin (a standard cotter pin not shown) removed from the locking cotter pin hole 20, so that the cutter is in condition for operation. The cutter, as shown, is usually carried on a bracket or in a pocket associated with the unit being dropped, and supported in a position in which the pilot chute line 17 can be freely pulled to withdraw the connection eye 16.

The sectional view of Figure 2 reveals the firing mechanism indicated generally by the numeral 21, the cartridge indicated generally by the numeral 22, and the cylindrical knife 23 within the tubular housing 24 of the explosive cutter 10. During assembly, the firing mechanism assembly 21 is introduced through the open firing end 15, and held in position against a counterbore 25 by means of a snap ring 26 seated in an internal annular :groove 27. The cartridge 22 and the knife 23 are introduced through the cutting end 12 and located in a proper position by an assembly locating screw 28, which threads through the hole 29 in the wall of the tubular housing 24 and projects inwardly into an external annular groove in the cartridge 22. After assembly, the cutting end 12 is closed by means of a closing disc 31 which seats against a counterbore 32 and is held in position by means of a snap ring 33 received in the internal annular groove 34.

The cartridge 22 functions as both fuse and propulsion means for the knife 23. The cartridge is housed in a tubular housing 35, which is reduced in diameter at the cutting end 36 to receive the cylindrical skirt 37 of the cylindrical cutting knife 23.

At the firing end of the cartridge 22, an exposed primer 39, lodged in a recess 40 communicates through a restricted passage 41 with an explosion chamber 42. A delay train 43, comprised of a series of slow burning pellets, usually about two seconds each, is located in the central passage 44 and provides a powder train from the empty explosion chamber 42 to a flash passage 45 and a black powder explosive propellant 4-6, just back of the cutter knife 23. It will be apparent that when the primer 39 is fired, the flash will pass through the passage 41, fill the combustion chamber 42, ignite the delay train 43.

The delay train 43 requires a precise number of seconds to burn from one end to the other during which the dropped object experiences free fall, trailing only the pilot chute, which must serve later to pull open the main parachute when its ree'fing line has been cut by the explosive cutter 10. At the end of the burning period for the delaytrain 43, the fire from the delay train 43 flashes through the hole 45, and the propellant charge 46 exploded. The cylindrical cutter knife 23 is propelled downward (as viewed in Figure 2) and travels like a bullet through the barrel of a gun to sever the reefing line 11 at reefing line holes 13 and 14, thus 'releasing the main parachute.

The firing mechanism 21 is principally supported in and a firing pin cylinder 50, which has a base flange 51' seated against the counterbore 25. The axial bore 52 down the center of the firing pin cylinder 50 carries a reciprocably movable firing pin 53, comprised of a pull section 54 and a firing section 55, seen in the perspective view of Figure 3.

The pull section 54 and the firing section 55 are locked together by the hooked ends of a breakaway joint 56 which can be unhooked only by the withdrawal upward (viewed in Figure 2) of the pull section 54. Movement of the firing pin assembly 53 toward the primer 39 is prevented by a shoulder 57 on the pull section 54 just under the connection eye 16.

The firing section 55 carries a disc-shaped firing head 58 with a striking point 59 at its firing end adjacent the primer 39 of the cartridge 22. The firing head 58 is adapted to ride like a piston along the interior walls of the tubular housing 24.

The assembly of the firing pin cylinder 59 and the firing pin 53 is enclosed in a helical firing spring 60, which seats on the inner side of the base flange 51 and the underside of the firing head 58, an annular shoulder 61 being providedat the underside of the firing head 58 to firmly locate the spring 60.

When assembled, as shown, the spring 60 is under a moderate compression so as to tightly hold the firing pin assembly 53 in position, and prevent it from rattling. However, the compression is so small that if the firing pin 53 were somehow broken and released, the spring would not urge the striking point 59 against the primer 39 with a sufiicient force to fire the cartridge 22. Thus, it will be seen that the explosive cutter here disclosed is not a prearmed assembly. However, the safety screw 18 has been provided in order to comply with possible military specifications, although it is believed to be unnecessary in the explosive cutter design of the invention.

Preferably, the device is safety locked by means of an ordinary cotter pin (not shown) inserted transversely through the firing end 15 of the explosive cutter 10 through cotter pin holes 20, so as to engage the connection eye 16 and hold its shoulder 57 firmly against the underside of the base flanges 51 0f the firing pin cylinder 50.

After the locking cotter pin has been removed from the locking :cotter pin holes 20 to prepare the explosive cutter for operation, the resistance of the spring is sufficiently great to prevent accidental manual operation, more than a ten pound pull being required to compress it. However, when the required pull is imparted to the connection eye 16 by the pilot chute, a pull equivalent to a twenty pound weight dropped three inches, at test, the pull compresses the spring 60 and for the first time introduces the potential energy required to impel the firing section 55 of the firing pin 53 down the interior of the tubular housing '24 with sulficient force to detonate the primer'39.

The same pull which arms the device retracts the firing head 58 toward the firing end 15, almost until the annular shoulder 61 abuts against the end of the firing pin cylinder 50, and retracts the breakaway joint 56 upwards until it is free-of the firing 'pin cylinder which holds it in position. The breakaway joint or coupling 56 immediately uncouples the pull section 54 from the firing section 55, which reverses and :accelerates toward the primer 39 under theimpetus of the energy stored in the spring 60.

It will be understood that the invention is not limited to the particular details shown. For example, other types of cutting knife 23 can-easily be used, including an oblique guillotine type of knife for producing progressive cutting action, although this would scarcely .be necessary except in the .case of extremely heavy reefing lines or wires. As already mentioned, the safety screw 18 is only an additional safety feature and is not indispensable to the proper functioning of the invention. Various arrangements of connection 'to' the pull section '54 or of shielding thereofby the firing end 15 maybe devised if desired, althoughthe construction'shown is preferred.

While I have shown, described, and pointed out the fundamental novel features'of-theinvention as applied to one specific embodiment, it will be understood that various omissions and substitutions and changes in the form and detail of the device as illustrated and in their operation may be made by those skilled in the art without departing from the spirit and scope of the invention. It is my intention, therefore, to be limited only by the scope of the following claim.

I claim:

In an explosive parachute line cutter of the type in which a piston-type cutter knife at the cutting end of a tubular housing is impelled against a reefing line by a delay train explosive means a predetermined time after firing, a firing means which includes: a transverse partition in said tubular housing spaced from the starting end of said delay train to provide an explosion chamber; a primer means positioned in a recess on the firing end side of said partition, said primer means being in communication with said explosion chamber through a restricted opening in said transverse partition; a firing pin cylinder supported in the firing end of said tubular housing coaxially therewith but with an annular space between the exterior of said cylinder and the interior of said housing, said firing pin cylinder having a base of enlarged diameter seating against a counterbore shoulder in said firing end; means for holding said firing pin cylinder firmly against said shoulder and said firing end; a pull section member having a connection means disposed towards the firing end of said tubular housing and a breakaway coupling means of reduced diameter extending from said connection and closely received in the end of said firing pin cylinder, a shoulder being formed between said connection means and said breakaway coupling means to limit the length of said pull member received in said firing pin cylinder; a firing pin member closely received in said firing pin cylinder and longitudinally slidable therein, and including coupling means mating with the breakaway coupling means of said pull member, and adapted to break away when said pull member is withdrawn from the end of said cylinder toward the firing end of said tubular housing; a striking head piston at the end of said firing pin member, said piston being reciprocable in said tubular housing adjacent said transverse partition; a helical spring means disposed in the annular space around said firing pin cylinder and around the part of said firing pin member projecting from said firing pin cylinder, and seated at one end against the base of said firing pin cylinder and at the other end against said striking head on the end of said firing pin member; a removable safety screw received in the side wall of said tubular housing between said transverse partition and said striking head piston; and a striking head projecting from said striking head piston toward said primer, said striking head being shorter in projecting length than the separation provided between said transverse partition and said striking head piston by said safety screw.

References Cited in the file of this patent UNITED STATES PATENTS 214,041 Huntington Apr. 8, 1879 2,581,695 Frieder et al. Jan. 8, 1952 2,665,163 Gross Jan. 5, 1954 2,742,697 Gross Apr. 24, 1956 2,755,550 Benjamin July 24, 1956 FOREIGN PATENTS 866,767 France June 9, 1941 888,864 France Sept. 20, 1943 

